A prior art midget rotary power shovel comprises, as illustrated in FIG. 2, an upper rotary member 2 rotatably disposed on a lower travelling body member 1 capable of self-travelling and a service machine 3 mounted onto the upper turning body 2.
The service machine 3 comprises a boom 5 capable of moving and lowering by a boom cylinder 4, an arm 7 mounted on a tip end of the boom 5 and rotatable by an arm cylinder 6 and a bucket 9 capable of being turned by a bucket cylinder 8. An offset mechanism 10 is provided on the boom 5 so that the arm 7 and the bucket 9 are movable laterally of the power shovel as illustrated in an imaginary line of FIG. 3.
If the arm 7 and the bucket 9 are turned with the service machine 3 being upright as illustrated in FIG. 2, a tip end of the backet 9 is liable to interfere with an operation room, etc. in an interference region as hatched in FIGS. 2 and 3.
Accordingly, there have been conventionally employed, as illustrated in FIG. 4, a solenoid valve 14 positioned between a cylinder 12 interlocked with an operation lever 11 and a control pump 13, a controller 15 for issuing a signal when the bucket 9 reaches a critical region ahead of the interference region to thereby open the solenoid valve 14 and forcibly return the solenoid valve 14 to a neutral position so that the service machine 3 is stopped.
However, inasmuch as the prior art service machine stopping apparatus has a structure to return a spool of the solenoid valve 14 to a neutral position by a return spring 16 provided inside the cylinder 12, there is a likelihood that the temperature of the working fluid is liable to affect the return speed of the return spring 16 or the engine speed or an operation method can affect the speed of the service machine. Hence, there is a drawback in that the stop time of the service machine is varied so that the stop position of the service machine is not stable to thereby vary the operation range.
Accordingly, the present invention is to provide a service machine stopping apparatus capable of solving the problem of the prior art service machine, reducing the delay of the stop time of the service machine to thereby ensure the stable and wide operation range.